This invention relates to an improvement of the subject-matter disclosed in the patent application of Philip C. Jacobs, Jr. filed Sept. 25, 1978, Ser. No. 945,542 for SOLDERLESS FUSE TERMINAL. The invention disclosed in that application is predicated on the properties of fuse casings of certain synthetic resins, more particularly fuse casings as described in U.S. Pat. No. 3,979,709 to Daniel P. Healey, Jr., Sept. 7, 1976 for ELECTRIC FUSE HAVING A MULTIPLY CASING OF SYNTHETIC-RESIN-GLASS CLOTH LAMINATE. Speaking more generally, the present invention is applicable to casings of synthetic resins which can be significantly deformed on account of their elastic properties, or on account of their memory, i.e. the tendency to assume, after deformation thereof, the shape and configuration they originally had. The subject-matter of the above patent application of P. C. Jacobs, Jr. is limited to the same kinds of casing materials.
A fuse as disclosed by Jacobs includes a tubular deformable casing of a synthetic resin having a rim and a fusible element inside said casing bent over said rim and having a portion engaging the outer surface of said casing. A fuse as disclosed by Jacobs further includes a ferrule mounted on said casing and having a radially inwardly directed indentation in registry with said portion of said fusible element on the outer surface of said casing. The aforementioned indentation engages and deforms the portion of the fusible element on the outer surface of said casing, exerting such a pressure against said portion of said fusible element outside said casing to establish an electrically conductive solderless pressure joint between the portion of the fusible element outside of the casing and the indentation in the ferrule.
As explained in the above patent application of Jacobs, best results can be achieved only if there is a metallic back-up for the indentation in the ferrule. Such a back-up is provided by recessing the end surface of the ferrule into the casing or, in other words, by providing the ferrule with an annular portion situated axially outwardly of the rim of the casing, and with a circular portion, or re-entrant portion, situated inside of the casing.
Such special ferrules are more expensive to manufacture than standard ferrules having end surfaces situated in one single plane.
In many instances such special ferrules cannot be applied since they mean a reduction of the internal volume of the fuse that is available for accommodating the fusible element and the pulverulent arc-extinguishing filler.
Another disadvantage of the design proposed by Jacobs resides in the fact that it calls for a reduction of the active length of the fusible element equal to the depth of the cavity formed by each of two ferrules.
There is, therefore, an urgent need to provide a fuse having all the advantages of Jacobs, but none of its disadvantages.
The present invention complies with these requirements.